Electronic musical instruments provided with a circuit for generating a tremolo effect

ABSTRACT

PART OF TONE SIGNALS SELECTIVELY DRAWN OUT OF TONE GENERATORS BY OPERATION OF A KEYBOARD SECTION IS SUBJECTED TO RECITIFICATION AND DIFFERENTIATION TO OBTAIN A TRIGGER SIGNAL WHEN THE TONE SIGNALS RISE. THE TRIGGER SIGNAL IS SUPPLIED TO THE BASE OF EITHER OF FIRST AND SECOND TRANSISTORS JOINTLY CONSTITUTING AN ASTABLE MULTIVIBRATOR TO TRIGGER IT TO DRAW OUT MODULATING SIGNALS WHICH RISE SIMULTANEOUSLY WITH MUSICAL TONE SIGNALS. THE MODULATING SIGNALS MODULATE THE MUSICAL TONE SIGNALS IN AMPLITUDE TO OBTAIN A DISTANCT TREMOLO EFFECT.

Feb, 13, 1973 AKIHISA TAKEYAMA ELECTRONIC MUSICAL INSTRUMENTS PROVIDED WITH A CIR CUIT FOR GENERATING A TREMOLO EFFECT Filed Oct. 22, 1971' Q? OUTPUT E El v: H

mm mo m? w w United States Patent 3,716,648 1 ELECTRONIC MUSICAL INSTRUMENTS PRO- VIDED WITH A CIRCUIT FOR GENERAT- ING A TREMOLO EFFECT Akihisa Takeyama, Hamamatsu, Japan, assignor to Nippon Gakki Seizo Kabushiki Kaisha, Hamarnatsu-shi, Shizuoka-ken, Japan Filed Oct. 22, 1971, Ser. No. 191,649 Claims priority, application Japan, Oct. 26, 1970, 45/ 106,303 Int. Cl. Gl1 1/04 U.S. Cl. 841.25 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to electronic musical instruments and more particularly to a tremolo modulation circuit used therewith.

Electronic musical instruments are generally provided with circuits for generating a variety of effects to enable performance to be carried out in diverse forms. Among such circuits is one for producing a tremolo effect.

With electronic musical instruments using a tremolo modulation circuit of the prior art, musical tone signals conducted from the tone generators to a circuit for producing a tremolo effect by amplitude modulation through the keyboard section and tone coloring filter are subjected to amplitude modulation on the circuit by modulating signals supplied from a low frequency oscillator. The tone signals thus modulated are brought to a loud-speaker through an amplifier.

The amplitude modulating signals from the low fre quency oscillator are generally of saw-tooth type. Therefore, tone signals modulated by the signals displays a mandolin effect. Since the amplitude modulation circuit is continuously supplied with modulating signals, the rise time point of the musical tone signals will not always coincide with the rising point of the saw-tooth wave. Thus it often happens that there is produced tremolo effect imparted tone signals which start at a point of time during the period of the saw-tooth wave signal but not at the rising point thereof, resulting in the indistinct rise of musical tone signals when the keys are depressed and in consequence the occurrence of untruthful tones.

SUMMARY OF THE INVENTION It is accordingly the object of this invention to provide a tremolo modulation circuit for electronic musical instruments wherein the musical tone signals start by the depression of keys, just when the amplitude modulating signal exhibits a maximum amplitude, thereby creating a distinct tremolo effect.

To this end, the present invention, has separate circuit means disposed between the keyboard section for selectively drawing out tone signals from the tone generators and the low frequency oscillator for supplying modulationsignals to an amplitude modulation circuit. The circuit means generates a trigger signal at the rise of tone signals selectively supplied from the keyboard section and ice conducts the trigger signal to the oscillator to cause the rise of the modulating signals to coincide with that of the tone signals. This circuit means may include a rectification circuit and a differentiator connected thereto. Further, the low frequency oscillator may be an astable multivibrator formed of first and second transistors.

Output from the differentiator, namely, a trigger signal is supplied to either of the two transistors constituting the astable multivibrator to control the rise of a modulation signal from the astable multivibrator, thereby making the rise coincide with that of tone signals from the keyboard section. Modulating signals from the astable multivibrator modulate tone signals in amplitude. Coincidence between the rise of musical tone signals thus modulated and that of modulating signals realizes a distinct tremolo effect.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram embodying this invention; and

FIGS. 2A, 2B and 2C present wave forms of signals illustrative of the operation of the circuit of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, tone signals are selectively drawn out of tone generators 1 by the key switches of a keyboard section 2 and conducted to tone coloring filters 3 to be converted to musical tone signals having particular tone colors. Output of the tone coloring filters 3 is coupled to the input terminal 14 of an amplitude modulation circuit 4. The input terminal 14 is connected to the base of an amplifier transistor Tr the collector output of which is connected to the base of an emitter follower transistor Tr The emitter output of the latter transistor Tr is coupled to the drain of a field effect transistor Tr the source of which is connected to the base of an amplifier transistor Tr The collector output of this transistor Tr, is coupled to the output terminal 16 of the amplitude modulation circuit 4. The gate of the field effect transistor Tr, is connected to the modulation input terminal 15 of the amplitude modulation circuit 4.

A low frequency oscillator 5 may include an astable multivibrator consisting of first and second active elements, or transistors Tr and Tr As is well known, when the first and second transistors Tr and Tr are alternate ly rendered conductive and nonconductive, there is drawn out a saw-tooth wave signal A shown in FIG. 2A from the base 11 of transistor Tr After amplified by a transistor TF7, the saw-tooth wave signal A is conducted to the emitter follower transistor Tr The emitter output of the emitter follower transistor Tr is coupled to the input terminal 15 of the amplitude modulation circuit 4 through a variable resistor 13 to vary the amplitude of the saw-tooth wave signal A for modulation.

When, in the circuit of the aforesaid arrangement, the saw-tooth wave signal A from the astable multivibrator 5 is supplied to the gate G of the field effect transistor Tr of the amplitude modulation circuit 4, then the impedance across the drain D and source S of the transistor Tr periodically varies, causing musical tone signals conducted to the input terminal 14 of the amplitude modulation circuit 4 to be drawn out of the source S in the amplitude modulated form as illustrated in FIG. 2B. The tone signals thus modulated is amplified by the transistor Tu, and conducted to the output terminal 16 of the circuit 4.

On the other hand, part of tone signals from the keyboard section 2 is rectified by a rectification circuit 8. The rectified output is then differentiatedby a differentiation circuit to obtain a trigger pulse signal at the rise of the tone signals. A negative trigger signal is supplied,

3 as shown in FIG. 2C, to the base of one transistor Tr included in the astable multivibrator 5 through a diode 10. Accordingly, the saw-tooth wave signal A from the astable multivibrator 5 is always made to rise upon key operation. That is, since the negative trigger pulse instantly renders the transistor Tr of the astable multivibrator 5 nonconductive and the transistor Tr thereby conductive, there can be obtained the saw-tooth wave signal A from the outset. Though there is required a period of 6 to 8 milliseconds for the transistor Tr to be rendered nonconductive and the transistor Tr to be rendered conductive after kep operation, such time delay presents substantially no practical problem. Even when, therefore, the key is depressed, as shown in FIG. 2, during the period of the saw-tooth wave signal A, the negative trigger signal C is simultaneously supplied to the astable multivibrator 5, so that the sawtooth wave signal A again begins to rise from its lowest level. Accordingly, the key depression substantially coincides with the maximum amplitude of the modulated signal B, obtaining a normal tremolo modulation.

What is claimed is: 1. An electronic musical instrument comprising: tone generators for producing tone signals; a keyboard section connected to said tone generators to select desired tone signals; tone coloring filters connected to the output of said keyboard section to convert tone signals selected by said section to musical tone signals; circuit means connected to said tone coloring filters to amplitude modulate musical tone signals obtained from said filters; low frequency oscillator means connected to said amplitude modulation circuit means to supply modulating signals thereto; and further circuit means connected between said oscillator means and said keyboard section to generate a trigger signal coinciding with the rise of tone signals selected by said keyboard section and supply said trigger signal to said oscillator means to cause the rise of said modulating signals to coincide with the rise of said tone signals.

2. An electronic musical instrument according to claim 1 wherein said amplitude modulation circuit means includes a field effect transistor having a drain, source and gate; and said drain is supplied with musical tone signals and said gate with said amplitude modulating signals, obtaining amplitude modulated musical tone signals from said source.

3. An electronic musical instrument according to claim 2 wherein said amplitude modulating signals are of the saw-tooth wave type.

4. An electronic musical instrument according to claim 1 wherein said low frequency oscillator means is an astable multivibrator formed of first and second transistors, and said trigger signal is supplied to either of saidfirst and second transistors.

5. An electronic musical instrument according to claim 1 wherein said low frequency oscillator means include means for controlling the amplitude of amplitude modulating signals being conducted to said amplitude modulation circuit means.

6. An electronic musical instrument according to claim 1 wherein said last-named means includes means for rectifying tone signals from said keyboard section and means connected to said rectifying means to differentiate the rectified signal.

References Cited UNITED STATES PATENTS 3,603,714 9/1971 Adachi 84-125 3,626,078 12/1971 Sekiguchi 84--1.24 3,593,187 7/1971 Dodds 841.24 X 2,899,644 8/1959 Leslie 841.25 X 3,510,567 5/1970 Fisher 841.25

RICHARD B. WILKINSON, Primary Examiner U. WELDON, Assistant Examiner U.S. C1. X.R. 841.24 

